package JUC.lock锁;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

/**
 * @author CKC
 * @DateTime 2021/3/31 15:34
 * 题目：实现一个自旋锁
 * *    自旋锁的好处  循环比较直到成功为止，没有类似wait的阻塞。
 * *    通过CAS操作完成自旋锁，A线程先来调用myLock自己持有锁5秒钟，B随后进来后发现
 * *    当前有线程持有锁，不是null，所以只能通过自旋等待，直到A释放锁后B随后抢到。
 */
public class SpinLockDemo {
    
    /**
     * 原子引用线程
     */
    AtomicReference<Thread> atomicReference = new AtomicReference<>();
    
    public void myLock() {
        Thread thread = Thread.currentThread();
        System.out.println(Thread.currentThread().getName() + "\t come in ");
        while (!atomicReference.compareAndSet(null, thread)) {
//            System.out.println("-----");
        }
        System.out.println(Thread.currentThread().getName()+"\t get Lock...");
    }
    
    public void myUnlock() {
        Thread thread = Thread.currentThread();
        atomicReference.compareAndSet(thread, null);
        System.out.println(Thread.currentThread().getName() + "\t invoked  myUnlock()");
        
    }
    
    public static void main(String[] args) {
        SpinLockDemo spinLockDemo = new SpinLockDemo();
        new Thread(() -> {
            spinLockDemo.myLock();
            try {
                TimeUnit.SECONDS.sleep(5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            spinLockDemo.myUnlock();
        }, "AAA").start();
        
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        new Thread(() -> {
            spinLockDemo.myLock();
            
            spinLockDemo.myUnlock();
        }, "BBB").start();
    }
}
